The present invention relates to a Huffman decoder as a kind of variable-length decoder for compressing an image signal, and more particularly, to a Huffman decoder of a look-up table type where the size of a search memory is smaller than ever.
By the compression algorithms such as MPEG, JPEG, pX64(H.261) and the like, as international standards for multimedia, a DCT-converted image signal is variable-length-encoded for transmission. Thus, Huffman decoding is used at the receiving end to decode variable-length code into the original fixed-length code. The conventional Huffman decoder for multimedia representatively uses such methods as tree searching and a look-up table. Here, Huffman decoding, as a kind of variable-length decoding, receives variable-length encoded code for restoration to fixed-length code.
For example, the variable-length code input for one fixed-length output word is generally composed of 2-24 bits. Theoretically, the length of an input string for a fixed-length output word of n bits can be expressed as 2 to 2.sup.n -1 bits.
In the conventional Huffman decoding, when the tree search method is used, the size of the search memory required for code conversion can be minimized. However, the search time is relatively long due to the characteristics of tree searching. As a result, it is difficult for the tree search method to be applied to an apparatus requiring fast processing, e.g., to digital television, HDTV or the like.
Meanwhile, when the look-up table method is used, the search time can be reduced. However, there is a problem that a die area is increased in manufacturing VLSI due to the increase of memory size for a table search.